try this,assuming viewer is your TreeViewer,but it does not work when the mouse was actioned on another control.
viewer.getTree().addMouseListener(new MouseListener() {
@Override
public void mouseDoubleClick(MouseEvent e) {
// TODO Auto-generated method stub
}
@Override
public void mouseDown(MouseEvent e) {
// TODO Auto-generated method stub
}
@Override
public void mouseUp(MouseEvent e) {
// TODO Auto-generated method stub
System.out.println("Mouse UP");
}
});